Memory devices are typically provided as internal, semiconductor, integrated circuits and/or external removable devices in computers and other electronic devices. There are many different types of memory including random-access memory (RAM), read only memory (ROM), dynamic random access memory (DRAM), synchronous dynamic random access memory (SDRAM), phase change random access memory (PCRAM), and flash memory, among others.
Flash memory devices can be utilized as volatile and non-volatile memory for a wide range of electronic applications. Flash memory devices typically use a one-transistor memory cell that allows for high memory densities, high reliability, and low power consumption. Uses for flash memory include memory for solid state drives (SSDs), personal computers, personal digital assistants (PDAs), digital cameras, cellular telephones, portable music players, e.g., MP3 players, and movie players, among other electronic devices. Data, such as program code, user data, and/or system data, such as a basic input/output system (BIOS), are typically stored in flash memory devices.
Two common types of flash memory array architectures are the “NAND” and “NOR” architectures, so called for the logical form in which the basic memory cell configuration of each is arranged. A NAND array architecture arranges its array of memory cells in a matrix such that the control gates of each memory cell in a “row” of the array are coupled to (and in some cases form) an access line, which is commonly referred to in the art as a “word line”. However each memory cell is not directly coupled to a data line (which is commonly referred to as a digit line, e.g., a bit line, in the art) by its drain. Instead, the memory cells of the array are coupled together in series, source to drain, between a common source and a data line, where the memory cells commonly coupled to a particular data line are referred to as a “column”.
Memory cells in a NAND array architecture can be programmed to a desired state. For example, electric charge can be placed on or removed from a charge storage node of a memory cell to put the cell into one of a number of programmed states. For example, a single level cell (SLC) can represent two states, e.g., 1 or 0. Flash memory cells can also store more than two states, e.g., 1111, 0111, 0011, 1011, 1001, 0001, 0101, 1101, 1100, 0100, 0000, 1000, 1010, 0010, 0110, and 1110. Such cells can be referred to as multilevel cells (MLCs). MLCs can allow the manufacture of higher density memories without increasing the number of memory cells since each cell can represent more than one digit, e.g., more than one bit. For example, a cell capable of representing four digits can have sixteen programmed states.
A memory system can include a host, such as a computer, and various types of memory used in various combinations to provide memory for the host. For example, a memory system can include a host and an external memory device coupled to the host. The external memory device can be, for example, a flash memory device. Additionally, the external memory device can be a removable memory device coupled to the host through an interface, such as a USB connection, for example.
The external memory device can include, e.g., store, system boot code used to boot the memory system. For example, responsive to a booting event of the memory system, the boot code, e.g., data representing the boot code, can be loaded from the external memory device to the host, and the host can use the boot code to boot the memory system. However, the boot code stored in the memory device may be visible to a user of the host.